Formulae can be personalized to add a personal touch in their expression. This can be completely unique by individual, or a theme or motif adopted by a certain branch, mentor or institution of tutelage. Keep in mind, that such personalized elements are likely to give away tell-tale signs of the origins of learning or use in a setting. An formulae which is personalized, can be used without adding the personal touches to it when used.
Uncommon: Personalization is generally not part of standardized traditions that impart occult knowledge through tutelage (personal or institutional). The knowledge is most often delivered in the most direct form, with as few barriers to the fastest uptake of the knowledge as possible. Learning this way is the most efficient. Deeper understanding may come from philosophical and practical testing of edge cases and obscure knowledge, but the results of occult formulae are recognizable from their common expressions. This may vary by setting and/or institutions in it. More often than absolute personalized differences are thematic ones from a specific source (institutional or master-apprentice tradition). These often are on purpose in order to promote the source from which they came – essentially a form of brand recognition.
See ©Dnd Tasha’s Cauldron for their initial take on Personalized Magic.
Generally, the Arcana skill will cover recognizing the source of the personalization, assuming the tutelage is widely known.